Spin excitations under fields in an anisotropic bond-alternating quantum S=1 chain: contrast with Haldane spin chains (original) (raw)

Inelastic neutron scattering on the S=1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4 reveals distinct spin excitation behaviors under varying magnetic fields. Below a critical field, Hc, normal Zeeman splitting is observed with unusual behavior in higher modes due to low-lying two-magnon continua, which contrasts the behavior of Haldane-gap materials where multiple excitations are present. Above Hc, only one excitation mode survives, illustrating the fundamental differences between dimerized and uniform spin chains.